Re: Resource Fork as Extended Attributes
Re: Resource Fork as Extended Attributes
- Subject: Re: Resource Fork as Extended Attributes
- From: Chris Suter <email@hidden>
- Date: Fri, 24 Jul 2009 09:46:05 +1000
Hi Mark,
On Fri, Jul 24, 2009 at 2:35 AM, Mark Day<email@hidden> wrote:
> On Jul 22, 2009, at 6:59 PM, shailesh jain wrote:
>>
>> On HFS Plus, the maximum EA size is based on the node size of the
>> Attributes B-tree. By default, the node size is 8192, which results in a
>> maximum EA size of just over 3800 bytes. Resource forks (where the EA name
>> is "com.apple.ResourceFork") are actually stored as extents, and can be much
>> larger.
>
> Hmm. Atleast TN1150 seems to suggest that B-tree node size for Attributes
> file is 4KB (while for catalog file it is 8KB).
>
> We should update that to indicate that the default in Mac OS X is 8 KiB. We
> already had a bug report about needing to update TN1150 for more information
> on how the Attributes B-tree works (once it was finally implemented in Mac
> OS X). I added a note to that bug report that we also need to update the
> default node size for the Attributes B-tree.
> Thanks for pointing out the documentation bug.
Hmm. The code for newfs_hfs looks like it could do with improving too
(at least in the version I'm looking at): it takes parameters to
control the attribute node size yet doesn't do anything with them; it
doesn't create the attributes file. In fact on the version I'm using
it crashes if you try and use it. <rdar://problem/7088315>
There's also an issue with the Kernel where it assumes the B-Tree node
size is 8192 when calculating the maximum size of an inline extended
attribute, when in theory, it could be different. Not likely, of
course, but you'd want to check there's no panics because of it.
<rdar://problem/7088321>
Regards,
Chris
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